Opt Palaeoecological research in the Lower Rhine Alexander Kiink fV Contents Summary 1. Historical data on the insect fauna and chemistry of the river Rhine in the Netherlands 1.1. Historical data on the insect fauna of the Rhine 1.2. Chemical changes in the Rhine 2. Localities and methods 2.1. Localities 2.2. Methods 2.2.1. Collecting of the samples 2.2.2. Processing of the sediment 2.2.3. Analyses of the remains 2.2.4. Dating of the samples 2.2.5. Processing of the data 3. Results 3.1. Outline of the changes in the macro invertebrates of the river deposits 3.2. Possible effects of long-term changes in the temperature of the Rhine 3.3. The changing habitats in the Rhine and their effect on the insect fauna 3.4. Incidence of deformities in headcapsules of Chironomus larvae 3.5. Changes in the Diptera fauna of the Rhine 4. Description of two cores with of different origin: an example of floodplain stratigraphy 4.1. Description of a sediment core from a lake generated by a dikeburst 4.2. Description of a river deposit in the freshwater tidal belt in the western part of the Netherlands 5. Concluding remarks 6. References Acknowledgem e nt s Appendix List of the taxa found in the sediment samples, compared to those living in the Rhine today Figures 1. Tentative compilation of the pollution history the Rhine derived from direct and indirect evidence 2. The Rhine-Meuse riversystem in the Netherlands 3. Outline of changes in the insect fauna of the Rhine 4. Number of days with ice in the Rhine since 1780 5. Relative abundance of insect fauna living in the bottom, related to the inferred age of the sediment (old) and exuviae (recent) 6. The incidence of deformities in the headcapsules of Chironomus larvae related to the inferred (underestimated) sediment age 7. Changes in Diptera composition in the Rhine according to sediment samples and recent exuviae collections 8. Percentage of typical river insects in the sediment core of L. Schoonrewoerdse Wiel 9. Factor analyses of the samples and insects in a sediment core from the Nieuwe Merwede Tables 1. Sampling sites by type and date of sedimentation/sampling Summary This is an account of the first few years of palaeoecological river research by means of insect remains in the Netherlands. In 1983 the first floodplain samples from the river Rhine were analysed and since then, step by step,w e have been building up biological evidence concerning the Rhine in former days. This chapter should be considered as a report on the initial phase of this line of research in the Netherlands. As is symptomatic of ana new application in sience, numerous questions arise from the analysed material and very few answers that can be given. Nor do we fully comprehend the scope of palaeoecological river research. It is therefor that we decided to present the findings in a way that reflects the present state Dutch research. The topics discussed here include the historical facts on the insect fauna of the Rhine and its chemical changes insofar they can be derived from direct or circumstantial evidence. The methods of collecting, identifying, dating and dataprocessing are described.Th e main focus of this chapter .however, is on some interesting changes in the insect fauna which have been revealed by the sediment analyses and the problems that arise in tracing the factors responsible for these changes. Furthermore two cores with different insect communities are discussed, as examples of stratigraphy in the lower part of the Netherlands. The conclusive remarks look at the potentials of palaeoecological river research in respect to river restoration. 1. Historical data on the insect fauna and chemistry of the river Rhine in the Netherlands 1.1. Historical data on the insect fauna of the Rhine Data on the insects inhabiting the Rhine in the past are very scarce. From the most comprehensive record of riverine insects ( Albarda, 1889) we learn that the characteristic riverine Ephemeroptera, Plecoptera, Odonata and Trichoptera were still present in the 19th century. The best exponent of the Ephemeroptera is Palingenia longicauda. It burrowed in the claybanks in vast quantities (last recorded in 1907, Mol; 1985). The Plecoptera in the Rhine included the genera Oemopteryx, Iscperla and Chloroperla. These stoneflies became extinct in the eaiiy decades of this century (Geyskes.1940). Gomphus flavipes, a muddwelling dragonfly, was last collected in 1902 (Geyskes and Van Tol, 1983). The Trichoptera included , among others, Cheumatopsyche lepida, Lepidostoma hirtum, Psychomyia pusilla and many Hydropsyche species. The first two species have not been collected in the 20th century. The last record of Psychomyia pusilla dates back to 1933 (Fischer, 1934). Very little is known about the Diptera. Van Der Wulp (1877) notes that adult Simuliidae (only 4 species described) are very common on places near the rivers Rhine and Meuse. The chironomids mentioned in his work cannot be assigned to the typical river fauna. From the early records we can conclude that in the second half of the 19th and the first few decades of the 20th century a decline was observed in the larger insects. The present Rhine is deprived of Ephemeroptera (except Caenis species), Plecoptera, Anisoptera and Simuliidae. Apperently Trichoptera were absent from the Rhine for a long period of time, too. From 1978 on, however, a remarkable return of Hydropsyche contubernalis and some other caddis flies has been observed (Van Urk, 1984) 1.2. Chemical changes in the Rhine Evidence that early pollution of the Dutch rivers did not go unnoticed can be found in the following quotation from Velsen (1768): 'Our people have always been utterly indifferent to a vital part of this country, the rivers. We used them and abused them as we please, without any supervision whatsoever. If the rivers were to die tomorrow not a soul would care or be grieved. Instead of worshipping her as gods or saints, we treat thema s sewers, in which anyone may freely dispose of his wastes. This is what has caused their abominable state' We may conclude that the pollution referred to above was predominantly organic, since large-scale mining activities did not start until the middle of the 19th century. And it was not until the 20th century that steelproduction became a major industry and pesticides based on Hg and As were commonly used. In figure 1 the history of heavy metal pollution is inferred from analyses of old river sediments and stored soil samples from a lower branch of the Rhine. Organic pollution in former days has been deduced from the population statistics of the Netherlands. The first decades of the 20th century may be characterized as the onset of a steep rise in organic and heavy metal pollution in the Rhine. Since the Second World War an entirely new branch of industry has added its own characteristic compounds to the environment. With the development of the petrochemical industry the family of chlorinated hydrocarbons (DDT, PCBs, drins and dioxins) were released. In the 1960s and 1970s acetylcholinesterase inhibitors became in use as insecticides, resulting in concentrations in the Rhine of up to 50 u,g/l (Grève, 1980). The initial rise in chlorinated hydrocarbons (as EOCI) is not known as no analyses were made until 1973. In the mid seventies, however, concentrations as high as 30 u.g/1EOC I were measured (Grève, 1980). Concurrently, the pollution of the Rhine reached its maximum. Ever since improvements in oxygen content and a decline in micropollutants have been observed. The return of caddisflies in the Rhine, notably H. contubernalis could be the result of this improvement (Becker, 1987) (see section 1.1. and figure 1). Tentative development of the pollution in the R. Rhine lü ACh-inhibitors H EOCI EH Heavy metals • BOO 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 Maximum score/compound = 1.00 Fig. 1. Tentative compilation of the pollution history of the Rhine derived from direct and indirect evidence (sources CBS, 1983; Heuck-Van Der Plas (ed.), 1983; Grève, 1980; Government Institute for Sewage and Waste Water Treatment (RIZA), 1983; Dijkzeul, 1982; RIWA (Cooperating Rhine and Meuse Water Supply Companies), 1983 and 1984; Salomons and De Groot, 1978). 2. Localities and methods 2.1. Localities The sampling sites in the Rhine are listed in figure 2. (Figure 2 to be inserted here) Figure 2. The Rhine-Meuse riversystem in the Netherlands. The sampling sites are numbered according to table 1. Table 1. Sampling sites by type and date of sedimentation/sampling Number River Type Date 1 Rhine floodplain deposit - 1745 2 Nederrijn floodplain deposit - 1880 3 Nederrijn exuviae sampling 1981 4 Ussel sediment core ? 5 Ussel exuviae sampling 1986 6 Ussel sediment core ? 7 Waal exuviae sampling 1985 8 Waal suspended solids (> 100u.m) - 1984 9 Boven Merwede floodplain deposit 1914 1o 1o Nieuwe Merwede 9 sediment core 11 Nieuwe Merwede12 sediment core 1 2 Schoonrewoerdse Wiel sediment core 1750-1984 11 2.2. Methods 2.2.1. Collecting of the samples The sediment samples were collected in three different ways. - Sediment cores from the riverbed were taken by means of a mudcorer installed on a research vessel. The core from Schoonrewoerdse Wiel (nr. 12) was taken by means of scuba gear. - Floodplain deposits were collected with hand auger equipment for soil research. The augers were drilled into the soil until a layer of coarse sand was met, indicating the former riverbed. Since these layers contain hardly any remains of invertebrates, the samples were taken from the silt layer directly on top of the sand was taken for analyses.